This invention relates to watt-hour meters. In particular, the invention is directed to preventing the theft of electrical energy and alerting an electrical supplier to the fact that an electrical user has tampered with the meter.
An expensive and growing problem besetting utility companies is the theft of electrical energy achieved by meter tampering. One commonly known method for stealing electricity is to drive the metering movement backward. This is accomplished when the user inverts his watt-hour meter from its forward orientation by removing it from the socket, turning it upside down and replacing it in an inverted position. In this position the line conductors are connected in reverse, causing a phase reversal in the winding's magnetic field which then drives the metering movement backwards. Consequently, as electricity is used, the meter dials rotate backwards indicating reduced consumption, when in fact, electrical energy is actually being consumed.
One known method for preventing inversion, as described in U.S. Pat. Nos. 4,034,290 (Warren) and 4,104,588 (Westberry), is to provide meter mounting means and socket means that mate only when the meter is plugged into the socket in an upright position. However, this is economical only in new installations because of expenses involved in removing standard meter installations and replacing them with newly designed meters and connections.
Another known means to indicate tampering is the "red flag" indicator disclosed in U.S. Pat. No. 3,915,112 (Forester). The indicator is gravity actuated and thus an inherent problem with such a device is that any inversion of the meter could trip it, for instance during shipping. Once tripped, the meter cover seal must be broken and the cover removed to permit resetting the indicator before installing the meter. Since the meter cover seal is the manufacturer's guarantee of meter accuracy, the meter must be retested each time the seal is broken. This results in unnecessary delays and expenses.
U.S. Pat. No. 4,039,943 (Tapscott) discloses a gravity actuated switch for reversing the meter voltage winding connections when a meter is inverted thereby retaining the same rotational movement of the metering movement. This meter is relatively complex and accordingly expensive. Reference is made in Tapscott (column 1, line 38-45) to a meter by Westinghouse Electric Corporation Style No. 285A082G02 employing a detent assembly to prevent meter movement rotation in reverse. Such a device is mechanically liked to the motor assembly and is responsive to motor operation and is thus also complex and expensive.